General rule: if you don't know what a particular server does, you don't need it.
DNS stands for domain name service. It's what translates names like www.linuxquestions.org
into numeric Internet addresses. So long as you can connect to your ISPs DNS servers to resolve hostnames, you're safe.
NFS is Network File System. It's a way to share filesystems over a network. You don't need this.
Googling will give you a lot more details, if you're interested.